Biological re-colonization of sub-aerial boundaries of an ‘artificial construction-niche’ contaminated by iron mine tailings: laboratory bioassays

The ability of colonizer organisms to tolerate high metal concentrations is important to the restoration and rehabilitation of mining sites. We investigated colonization on modular cellular surfaces—artificial construction-niche—prepared by combining different proportions of iron mine tailings (8% tailing dam material), soil (90%), and cement (2%) through bioassays conducted under stable laboratory conditions of humidity, temperature, and light intensity. The establishment of microorganisms was measured using CO2-respirometry and microbiological assays. Sub-aerial communities grown on the experimental materials were composed of heterotrophic and phototrophic macro- and microorganisms. Four groups of phototrophic species were observed: cyanobacteria, algae, mosses, and ferns. The cyanobacteria comprised three genera: Phormidium sp., with branched filaments, Nostoc sp. and Pseudanabaena sp.; algae included Trentepohlia sp. (Chlorophyceae), a sub-aerial or terrestrial green algae. Macroscopic fungal hyphae were also observed. CO2 production occurred in all cellular modules due to the growth of bacteria, actinobacteria, and fungi. The presence of living organisms on these artificial construction-niche containing iron ore tailings was a promising finding as those colonizers could initiate the processes of primary succession and occupy significant portions of the sub-aerial surfaces, thus actively participating in weathering and soil formation to create new ecological niches for recuperating ironstone outcrop ecosystems.